Dozens of insect species live in and around trees and take flight at some point in their life cycle. Some are destructive pests that can kill a tree in a few years, some are harmless nuisances that congregate on sunny walls in fall, and others are beneficial predators you actually want around. Knowing which type you’re looking at determines whether you need to act or simply leave them alone.
Emerald Ash Borer
The emerald ash borer is one of the most destructive flying tree pests in the United States. Native to Asia, it’s now widespread across the eastern U.S. and has been confirmed in Colorado, though it hasn’t yet reached California. The adult beetle is a metallic green, roughly half an inch long, and flies between ash trees during summer to lay eggs on the bark.
The real damage happens beneath the surface. Larvae feed under the bark, eventually girdling the tree by cutting off its nutrient supply. Ash trees typically die within two to four years of the first symptoms appearing. The telltale sign of an emerald ash borer infestation is small, D-shaped exit holes in the bark, each about the size of a BB. You may also notice increased woodpecker activity on a tree, crown dieback starting at the top, or bark that’s splitting and cracking over feeding sites. Several states restrict the transport of ash firewood to slow the spread.
Spotted Lanternfly
The spotted lanternfly is an invasive planthopper first detected in the U.S. in 2014. It feeds on over 70 species of vegetation, including hardwood trees, grapevines, hops, and ornamental plants. Adults are about an inch long with gray wings dotted in black spots; when they spread their wings, they reveal a flash of bright red underneath. They’re strong jumpers and capable fliers, often seen swarming in large numbers on tree trunks and branches.
Spotted lanternflies produce large amounts of honeydew, a sticky waste that coats leaves, bark, and anything beneath an infested tree. This honeydew promotes the growth of black sooty mold and attracts other insects. The pest is currently concentrated in the mid-Atlantic states and parts of the Midwest, with quarantine zones in place to prevent hitchhiking on vehicles and outdoor equipment.
Boxelder Bugs and Stink Bugs
If you’re seeing flat, reddish-black bugs flying around trees in fall, you’re likely dealing with boxelder bugs. They feed on the flowers, leaves, and seedpods of female boxelder trees and cause minimal damage to ornamental and fruit trees. In early fall, they congregate on sunny walls, especially western or southern exposures and light-colored surfaces, looking for warmth before overwintering. They’re harmless to humans and don’t cause structural damage.
Brown marmorated stink bugs behave similarly, clustering on warm surfaces in autumn. Originally from Asia, they’re invasive in the U.S. and do damage fruits, vegetables, and other plants. They release foul-smelling chemicals when threatened, and once one stink bug finds a good shelter spot, it secretes chemicals that attract others. Both species are more of a household nuisance than a serious tree threat, but stink bugs can be a real problem for gardens and orchards.
Clearwing Borers and Flatheaded Borers
Several species of wood-boring insects have winged adult stages that fly between trees to lay eggs. Clearwing borers are moths that resemble wasps, and their larvae tunnel into branches and trunks. Early signs of infestation include wilting at the tips of branches, crown dieback, and cankers or cracked bark at feeding sites. You may notice coarse, brown sawdust-like material (called frass) pushed out through bark cracks, sometimes mixed with oozing sap. When the adult moth emerges, it leaves behind an empty tan shell protruding from the bark.
Flatheaded borers, like the flatheaded appletree borer, are especially dangerous to small, stressed landscape trees. Flowering crab apples, hawthorns, and maples are vulnerable during the first year or two after transplanting. Trees weakened by drought, sun scald, soil compaction, or mechanical injury are the most likely targets. The adults leave D-shaped exit holes similar to those of the emerald ash borer. Dead or dying limbs will have numerous holes, and heavily infested bark becomes visibly cracked.
Aphids and Scale Insects
Aphids are tiny, soft-bodied insects that cluster on leaves and new growth. Most of the time they’re wingless, but when a colony gets overcrowded or food runs low, winged aphids are produced to fly to new host trees. In fall, some species produce winged males and females that mate and lay eggs on a winter host plant before dying. You’ll often notice aphids by the sticky honeydew they leave behind or by curling, yellowed leaves.
Scale insects are less obviously “bugs that fly,” but the males of many species are tiny, winged insects. Male armored scales have a single pair of wings and generally die shortly after mating. Female scales remain immobile on bark or leaves. Mealybugs follow a similar pattern: the females are wingless and covered in a white, waxy coating, while the males develop two wings. If you see tiny, gnat-like insects hovering near a tree with scale problems, those are likely the short-lived males.
Douglas-Fir Tussock Moth
The adult Douglas-fir tussock moth is a flying moth whose caterpillars chew the needles of spruces, Douglas fir, and true firs. During outbreaks, caterpillars can extensively defoliate a tree, starting with new growth at the top and working down to older needles. The top of a heavily damaged tree can be killed after just a single season of severe feeding. In urban areas, blue spruce is particularly affected.
Beneficial Flying Insects in Trees
Not every flying bug on your tree is a problem. Several beneficial species live in tree canopies and actively control the pests listed above.
- Lacewings: Light green, less than an inch long, with two pairs of delicate wings. Their larvae are voracious predators of aphids, scale insects, whiteflies, and thrips. Adults feed on insects, nectar, and pollen.
- Parasitic wasps: Tiny, solitary insects that are generally not dangerous to humans. They lay eggs on or inside pest insects like caterpillars, grubs, scales, and aphids. Most are smaller than an eighth of an inch and go unnoticed.
- Ladybugs: Both adults and larvae eat soft-bodied pests like aphids, mealybugs, and whiteflies. The spiny, dark-colored larvae are often mistaken for pests themselves.
- Dragonflies: Fast-flying predators that hunt mosquitoes, flies, and gnats on the wing, reaching speeds up to 30 miles per hour.
- Hover flies (syrphid flies): Resemble tiny bees but are harmless. Their larvae feed on aphids, making them valuable around infested trees.
Signs Your Tree Has a Problem
The most reliable indicators of a flying pest infestation are visible changes in the tree itself. D-shaped or round exit holes in the bark point to wood borers. Sawdust-like material at the base of the trunk or in bark crevices means something is tunneling inside. Sticky honeydew on leaves, branches, or the ground beneath the tree suggests aphids, scale insects, or lanternflies. Crown dieback that starts at the top and works downward is common with both borers and defoliating caterpillars.
Increased woodpecker activity on a particular tree is a strong clue, since woodpeckers are drawn to trees with larvae beneath the bark. Cracked or cankered bark over specific spots, especially on young or recently transplanted trees, often marks a borer’s feeding site.
Managing Flying Tree Pests
Healthy trees resist pest attacks far better than stressed ones. Deep watering several times a month from June through September, balanced fertilization, and avoiding mechanical damage to bark and roots all reduce vulnerability. Over-fertilizing can actually attract aphids by producing lush, tender growth.
Encouraging natural predators is one of the most effective long-term strategies. Flower gardens and unmowed areas near trees provide habitat for parasitic wasps, lacewings, ladybugs, and other beneficial insects that keep pest populations in check. Avoiding broad-spectrum pesticides like organophosphates and carbamates preserves these natural enemies. More targeted options include bacterial-based products that kill specific caterpillar larvae when ingested, clay compounds that irritate and repel insects, and virus-based treatments designed for individual pest species like codling moths.
For borers already inside a tree, options are limited once larvae are established beneath the bark. Pruning and removing infested limbs before adults emerge can reduce spread. For invasive species like the emerald ash borer, professional treatment with systemic insecticides applied to the trunk or soil may be necessary to save high-value trees. With spotted lanternflies, scraping egg masses from tree trunks during winter and using sticky bands to trap nymphs as they climb in spring are practical control measures.